The present invention relates to an apparatus for cooling a transfer mandrel, and more particularly is directed to a cooling apparatus provided on a parison heating station for prevention of the temperature rise in a transfer mandrel on which is mounted the thermoplastic resin parison for blow molding or draw-blow molding of hollow articles.
A draw-blow molding apparatus for making thermoplastic resin hollow articles of a type as illustrated in FIG. 1 is proposed in Japanese Laid-Open Patent Publication No. 93062/1979 or U.S. patent specification No. 4,214,860. In equi-spaced relationship along the periphery of a rotary heating table 1 a plurality of supporting portions 3 for transfer mandrels 2 are provided as indicated in FIG. 1. A parison 5 having a bottom is conveyed in the arrow direction by means of a conveyor 4, mounted on the top portion of the transfer mandrel 2 at the leading end portion of the conveyor 4, and heated to a draw-blowable temperature by means of an infra-red radiation heating means 6 while transferred in the arrow direction along with the rotary heating table 1. Subsequently the parison 5 riding on the transfer mandrel 2 is fed by means of a transfer table 7 to a draw-blow molding mold 9 provided on a molding table 8 rotating in the arrow direction, and molded thereon to a hollow article 10 having a predetermined shape. The hollow article 10, while it is transferred to an arm 12 provided on a rotary discharge table 11 together with the transfer mandrel 2 and travels in the arrow direction, is separated from the transfer mandrel 2 and delivered to the next step via a discharge chute 13, while the transfer mandrel 2 is engaged again with the supporting portion 3 on the rotary heating table 1.
As described hereinabove, the transfer mandrel 2 is circulated repeatedly through all the stations or steps, and during its circulation the temperature of the top portion 2a (refer to FIG. 2) thereof and its vicinity increases gradually and sometimes rises over the glass transition point of the resin forming the parison 5 (e.g. linear polyester resins such as polyethylene terephthalate) by radiation heating from a reflection panel 30 (refer to FIG. 2) and heat conduction from the heated parison or the like, although the device is designed so that the transfer mandrel (2) is not heated directly by the infra-red radiation heating means 6.
The above-mentioned temperature rise causes a temperature rise at the open end portion 5a of the parison 5 in contact with the top portion 2a of the transfer mandrel 2, which poses problems such as the deformation of the open end portion 5a during the heating step and the imperfect sealing between the open end portion 5a and the transfer mandrel 2 leading to a poor formed article obtained during the blow molding or draw-blow molding step. Further, since the deformation of the open end portion 5a and the imperfect sealing described above increase with the heat capacity of the infra-red radiation heating means 6, the infra-red radiation heating means of a relatively small heat capacity has to be employed so as to alleviate the above-mentioned problems, which brings about a disadvantage that the peripheral velocity of the rotary heating table 1 must be reduced so as to assure the sufficient heating of the parison 5, thereby leading to a low productivity.